Advertisement

Advertisement

BIG PHYSICS, BIG QUESTIONS –

Forum: Suck it and see! – The supremacy of practice over theory

By SUE BIRCHMORE

I’VE BEEN browsing through some old undergraduate notes. Castigliano’s
theorem, Poisson distributions, eigenvectors . . . it’s marvellously impressive-sounding
stuff. And, indeed, I’ve had occasion to use a fair amount of it in the
real world of industry. However, there always comes a point where mundane
reality breaks through any intellectual pretensions.

This was brought home to me very early on in my engineering career,
when I had a disagreement with my boss about how much force a beam in a
proposed design would be able to deflect. I had calculated a figure, and
recommended using a thicker beam; he didn’t believe my figures. The matter
was resolved by getting a steel rod of the required thickness out of the
stores, clamping it in a vice, dangling a weight on the end and measuring
the deflection, I emerged vindicated and with a rooted belief in the precedence
of cold steel over theory.

Looking through some other documents, I found some notes for a design
manual I wrote, a distillation of all I ever learnt about the design and
specification of springs. Coil springs are well-behaved, geometrical sorts
of animals, easily susceptible to theoretical analysis, but the potential
shapes for flat springs are as wide as the imagination of the designer.
Hence my pronouncement: ‘. . . however, in the case of complex designs,
it will frequently be quicker to manufacture samples and load test than
to attempt a rigorous theoretical analysis . . . ‘

Herein lies the difference between engineers and pure scientists. Engineers
are pragmatists at heart; we don’t really, fundamentally care about arriving
at the solution by elegant means, so long as it works, preferably as cost-effectively
as possible. This attitude shows up in some interesting solutions to practical
problems which I’ve encountered; solutions which were considered rather
infra dig by outside observers, but what the heck – they worked.

Advertisement

The problem of colour-coding wire-forms, for example. Cars use an awful
lot of bits of bent wire for linking door handles to latches, supporting
roof-linings and so on, and they have to be colour-coded for identification.
We had a lovely new numerically controlled machine to make them, with lots
of interconnecting mechanisms zipping up and down in sequence – very high-tech.
Proudly, we displayed our expensive investment to a representative from
one of our customers. He watched it for a few minutes. ‘Why,’ he asked,
‘has it got a felt-tip marker in the middle of it?’

Sure enough, gripped in one of the chucks which hold the various tools
to bend, nib and crop the wire, there was a bright yellow marker pen, going
up and down with every wire-form which whizzed through the machine.

‘Colour coding,’ we explained.

He looked pained. ‘Couldn’t you come up with something a bit more .
. . technical? Drip-feed paint or something?’

Yes, those sort of arrangements had been looked at. But in the end,
a felt-tip is cheap, isn’t messy, doesn’t clog, and is easily replaced when
it runs out. Who needs anything more technical? Then again, there were the
wavy washers for petrol caps. A wavy washer is, well, a washer with waves
in it, used as a sort of very short spring. To put some tension into a certain
design of fuel cap, we included a wavy washer. But the manufacturer of the
cap failed to specify the washer correctly, and the batch we made totally
failed to produce enough force to make the design work. A representative
from the cap manufacturer (our customer) turned up on the doorstep with
a boxload of washers and a harassed look on his face. ‘We’ve got to have
a couple of hundred that work before midnight,’ he announced tragically,
‘or the car production line will stop!’

Make some more? No time for that – it could take several hours to set
up the machine. In the end, it came down to the customer’s engineer and
me, down in the inspection pen, bending washers with our own fair hands,
and then squashing them down again (the springmakers’ term is ‘scragging’)
until they delivered the right force. Crude? Yes – but at least we emerged
with enough functional washers to keepthe production line going.

If there’s a moral to these tales, I suppose it’s that the concept of
appropriate technology applies in West Bromwich as much as it does in West
Africa. If the humble, low-tech method happens to be cheaper, quicker, more
energy-efficient or less polluting than the high-tech alternative, then
we shouldn’t be ashamed to use it.